#include <stdio.h>

int main(){
	int grade;

	printf("请输入成绩（0-100)\n");

	scanf("%d", &grade);

	grade /=10;
	switch(grade){
		case 10:
			printf("S\n");
			break;
		case 9:
			printf("A\n");
			break;
		case 8:
			printf("B\n");
			break;
		case 7:
		    printf("C\n");
		    break;
		case 6:
			printf("D\n");
			break;
		default:
			printf("F\n");
			break;
	}

	return 0;
}